The invention relates generally to sensors, and particularly to optical sensors and methods of making the same.
In recent times, there has been an increasing demand for optical sensors that can detect small amounts of analytes, such as proteins, DNA, toxins, and biological pathogens. Optical sensors based on microspheres have been used to detect the presence and/or concentration of small particles. Typically, in a microsphere based optical sensor, an optical fiber evanescently couples light to a microsphere. To assist in coupling light from the fiber into microsphere, the region of the fiber that is in close proximity to the micro sphere is tapered. The tapered end is aligned with the microsphere. An evanescent electromagnetic field associated with total internal reflection exists just outside the microsphere. This electromagnetic field decays exponentially as a function of distance, typically over a distance in a range from about 0.1 to 0.3 microns. The evanescent field is affected by changes in the surface properties of the microsphere, which in turn is influenced by the environment of the microsphere. The existing microsphere based optical sensors require high degrees of precision control of a gap between the tapered optical fiber end and the microsphere to achieve the optimal coupling efficiency.
Increasing the number of microspheres in a system has several commercial benefits such as multi-channel detection and higher throughput for bio-assay analysis. The existing coupling method translates into a limit on flexibility of expanding the applications of such optical sensors to larger systems, such as chip-scale sensors, and portable sensors. For example, as the number of microspheres increases, the complexity of the fiber alignment increases exponentially. In addition to the increasing complexity, positioning the microspheres having different sizes at the optimal locations and fixing the locations of the micro spheres is also challenging.
In addition to increasing the throughput, it is desirable to enhance the sensitivity of such optical sensors. For example, enhanced sensitivity may enable detection of individual protein molecules, or virus particle detection of extremely low concentration exposures that might otherwise go unnoticed, earlier warnings to exposures, a greater area of overall coverage with fewer sensors, to name a few.
Therefore, there is a need for an improved sensor that employs an effective and efficient way for coupling light to an optical resonator, which comprises one or more microspheres. Further, there is a need for sensor design that enables multi-channel detection for high throughput.